Radiation is commonly used in the non-invasive inspection of contents of objects, such as luggage, bags, briefcases, cargo containers, and the like, to identify hidden contraband at airports, seaports, and public buildings, for example. The contraband may include hidden guns, knives, explosive devices and materials, illegal drugs, and a nuclear or a “dirty” radioactive bomb, for example. One common inspection system is a line scanner, where the object to be inspected is passed between a stationary source of radiation, such as a gamma ray radiation or X-ray radiation, and a stationary detector. The transmitted radiation is detected and measured. Radiographic images of the contents of the object may be generated for inspection. The images show the shape, size and varying densities of the contents.
While the smuggling of guns, explosives and other contraband onto planes in carry-on bags and in luggage has been a well known, ongoing concern, a less publicized but also serious threat is the smuggling of contraband across borders and by boat in large cargo containers. Only 2%-10% of the 17 million cargo containers brought to the United States by boat are inspected. “Checkpoint Terror”, U.S. News and World Report, Feb. 11, 2002, p. 52.
Standard cargo containers are typically 20-50 feet long (6.1-15.2 meters), 8 feet high (2.4 meters), and 6-9 feet wide (1.8-2.7 meters). Air cargo containers, which are used to contain a plurality of pieces of luggage or other cargo to be stored in the body of an airplane, may range in size (length, height, width) from about 35×21×21 inches (0.89×0.53×0.53 meters) up to about 240×118×96 inches (6.1×3.0×2.4 meters). Large collections of objects, such as many pieces of luggage, may also be supported on a pallet. Pallets, which may have supporting side walls, may be of comparable sizes as cargo containers and use of the term “cargo conveyance” encompasses cargo containers and pallets. As used herein, the term container is meant to include, but should not be limited to, cargo, air cargo containers, pallets, luggage, and handheld carry-ons.
Atomic bombs and “dirty bombs,” which may use a conventional explosive and a conventional trigger to disperse radioactive material over a wide territory, are examples of nuclear devices that may be smuggled in cargo conveyances and smaller objects. These devices often include control and/or trigger electronics, such as timing devices or communications devices, that are used to detonate the explosive and/or trigger the nuclear device. Conventional explosive devices, comprising a trinitrotoluene (TNT), dynamite, and fertilizer based explosives, may also include control and/or triggering electronics. Radioactive, fissionable, fissile, and fertile materials that may be used to manufacture nuclear devices may also be smuggled.
Additionally, hazardous chemical and biological materials may be smuggled in containers in a similar fashion. Chemical agents, such as chlorine gas, mustard gas, phosgene, sarin and other nerve agents, for example, and biological agents, such as anthrax, small pox, tularemia, and hemorrhagic fever, for example, may be packaged and hidden in cargo conveyances and other objects for shipment across borders. Further, some chemical and biological agents may be smuggled inside a cargo conveyance or other objects in the form of an operational chemical or biological weapon. Similar to the explosive weapons, the chemical or biological weapon may also include control and/or trigger electronics, such as timing devices or communication devices. Such chemical and biological agents and weapons may be detected using chemical or biological sensors, as described, for example, in U.S. Pat. No. 6,610,977, U.S. Pat. No. 5,585,575, U.S. Pat. No. 6,711,939, and U.S. Pat. No. 6,834,533, which are incorporated by reference herein, in their entireties.
A variety of techniques are used to locate nuclear devices, nuclear materials, radioactive materials (that may not be nuclear materials), hazardous chemicals, hazardous biological agents in cargo conveyances. Although time consuming, manual inspection of the contents of the objects in a container may be highly effective in identifying hazardous targets. Additionally, identification of radioactive materials and nuclear devices and other weapons may be accomplished by passive inspection systems, such as a radiation detector.
Active systems that employ radiation to scan cargo and containers are often used. In one example of an X-ray scanning system, U.S. Pat. No. 5,524,133 discloses scanning systems for large objects, such as freight in a container or on a vehicle. In one embodiment, two stationary sources of X-ray radiation are provided, each emitting a beam that is collimated into a fan beam. The sources facing adjacent sides of the freight and the fan beams are perpendicular to each other. A stationary detector array is located opposite each source, on opposite sides of the freight, to receive radiation transmitted through the freight. The material content of the freight is thereby determined. Additional radiation systems for inspecting large cargo are described in U.S. Pat. No. 6,292,533, U.S. Pat. No. 5,917,880, and U.S. Pat. No. 5,638,420, for example.
Likewise, in U.S. Pat. No. 6,347,132 B1, a high energy X-ray inspection system for detecting nuclear weapons materials is described wherein an object is scanned by a high energy X-ray fan beam or pencil beam. To obtain additional information about the contents of the luggage, radiation detectors may be provided to detect scattered radiation, as described in U.S. Pat. No. 5,642,394, for example. Systems may combine detection of scattered radiation in addition to the detection of transmitted radiation.
Another technique to enhance the information that may be derived about the material composition of the contents of the objects is to scan the object with radiation beams having two different energy levels. A ratio of the attenuation detected at two different energy levels is indicative of the atomic numbers of the material through which the radiation beam passes. Dual energy systems enable better detection of plastic materials and illegal drugs. U.S. Pat. No. 5,524,133, which is incorporated by reference herein, describes a dual energy technique for identifying contents of an object.
Computed tomography (“CT”), as discussed in U.S. Pat. No. 5,567,552 for example, enables the reconstruction of the cross-sectional images of luggage contents, facilitating the identification of the items in the luggage. CT images also provide higher resolution, greater image contrast and greater sensitivity to characteristics of the object being scanned, than radiographs. Scanning methods, such as CT, may be used to generate images showing weapon control and trigger electronics, for example.
In contrast to the cargo container size ranges, typical airport scanning systems for carry-on bags have tunnel entrances up to about 0.40×0.60 meters. Scanning systems for checked luggage have travel openings that are only slightly larger. Since only bags that fit through the tunnel may be inspected, such systems cannot be used to inspect cargo containers. The low energies used in typical X-ray luggage and bag scanners are too low to penetrate through the much larger cargo containers. In addition, many such systems are too slow to economically inspect larger objects, such as cargo containers.
While known detection systems identify and locate potential threats, these systems do not provide a means for disabling the threat.